This invention relates in general to systems for removing contaminants from liquids and, more specifically to a system for removing particles, both heavy and light or buoyant particles from a liquid.
Water supplies for domestic drinking water, process water for chemical plants or other liquids are often contaminated with both heavy and light, buoyant, particles. These particles must be removed in a reliable, cost effective manner.
Many older water treatment plants use dual-media sand filtration systems that may not be acceptable under the newer water quality standards. In some cases, these systems can meet the standards through the use of properly mixed polymer chemical filter aids. The required expensive and complex polymer chemical mixing equipment requires constant attention, since the amount of the chemicals being added to raw water must be frequently readjusted to match the continually changing chemistry of the water being filtered. Slow sand filters require a considerable investment, but generally can be operate for longer periods without cleaning. Unfortunately, even with pre-treatment, both dual-media and slow sand filters fail to meet water quality standards for hours or several days after each backwash cleaning. Contaminates have been found to pass through a sand filter whenever water flow rates are changed and whenever the pump is stopped and turned on again. In order to meet standards, it may be necessary to pump filtered water to waste after every backwash cycle, disposing of thousands of gallons of water, until the filter "ripens" or compacts. Thus, these filter systems are less than desirable for use today.
Most conventional manually-cleaned filtration systems are oversized to extend the amount of time between cleanings. Since cleaning takes considerable time and may result in the problems described above, a lengthy time between cleanings has been considered highly desirable. Measuring differential pressure across the filter will indicate when the entire filter is clogged and in need of cleaning. This increase in differential pressure only occurs near the end of the filter run, giving little advance warning. Thus, there is a need for automatic self-cleaning filtration systems designed to automatically stop and run a backwashing cycle without inconveniencing the owner or operator. This will permit use of smaller, more optimum, filter sizes, where the decrease in differential pressure across the filter media begins immediately and gradually increases to the point where cleaning is necessary. This gradual increase in differential pressure would also allow the operator to calculate the exact volume of liquid flowing through the system and correlate flow volume to differential pressure, so that differential pressure readings can be used thereafter as a simple means of indicating flow rates.
Ozone and oxygen are sometimes mixed with water or other liquids to eliminate contaminants, in particular bacterial contaminants. In conventional ozone contact chambers, the ozone gas is applied at the base of a tall column. The ozone-oxygen bubbles float to the surface slowly, their upward movement slowed by the downward counter flow of the water stream. To achieve sufficient contact time before the water passes from the mixing column, the column must be extremely tall and is difficult to install in ordinary sized plant equipment rooms. The concentration of dissolved ozone-oxygen is undesirably diluted in the larger vertical columns. While ozone-oxygen contact in mixing chambers is generally effective, there is a need for improved mixing in smaller mixing vessels.
Cyclone separators are often used to separate heavy particulate material from liquids such as water. Typical of such cyclone systems is that described by Laval in U.S. Pat. No. 3,568,837. In such separators, a fluid stream is directed at high velocity into a cylindrical tank at an angle that cause the fluid to rotate at high speed, driving entrained particles to the wall from which the particles move downward into a conical tank bottom with a central valve for removing the collected particles. The liquid is removed from the center top of the tank. However, conventional cyclone suspended solids separators only remove heavy particles, with any entrained gases and light or buoyant particles remaining in the exiting fluid stream.
Thus, there is a continuing need for a separation system that can mix the liquid with ozone in a more effective manner, can separate entrained gases and light or buoyant particles from the liquid in addition to heavy particles and can post treat the liquid with further vortex separation and micron size particle separation and filtration if needed.